1. Department of Ecology and Evolutionary Biology, University of California at Los Angeles, Los Angeles, CA 90095–1606, USA.
2. Department of Vertebrate Paleontology, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA.
3. Department of Ecology, Evolution, and Marine Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.